Electric machines, such as motors, are used for a wide variety of applications. Knowing the frequency at which an electrical machine operates facilitates accurately determining whether the machine is malfunctioning. However, because of surrounding noise, it can be difficult to determine the operating frequency of the machine, particularly where the operating frequency of the machine is indistinguishable from the noise.
Sinusoidal modulated signals are important sources of diagnostic information for condition monitoring of certain types of machinery, such as electric motors. This is a well-known fact, as evidenced by such engineering publications as (1) Coley, Phillip. Fault Zone Analysis. Rotor. PdMA Corporation. Motor Reliability Technical Conference. May 6-8, 2003, Clearwater Beach, Fla.; (2) Variable Frequency Drives and Advanced Spectral Analysis, PdMA Corporation, 2003, p. 8-8-8-11; and (3) MCEmax Data Interpretation, PdMA Corporation, 2002, p. 199-206.
Essentially, a judgment is made about integrity of a rotor of an induction motor using certain spectral measurements. Rotor bars and/or end rings are shown to be damaged if the so-called Line Frequency Peak in the electric current spectrum of the motor has relatively high sidebands (i.e., spectral peaks at both of its sides), at a distance equal to the so-called Pole-Pass Frequency to the left and right of the Line Frequency Peak.
It is very common in practice that the sinusoidal modulated signal produced by a machine is obscured by noise, which always exists in real applications. This is especially true for smaller sidebands, which are even more prone to being obscured by noise. The ability to clarify a sinusoidal modulated signal from excess noise solves this problem, and thus enables successful condition monitoring.